I have over 500,000 digital music files and have recently gone to listening using headphones. Using the headphone audio controls is tedious, at best, so I am “equalizing” all the files. In other words, I open a file and use Effect►Amplify to adjust the amplification so that the New Peak Amplitude is -0.5. Then I export the file. However, if I open the new file, the amplitude has been adjusted by Audacity during the export process so that it is anywhere from -.2 dB to .5 dB different. How do I prevent this? Or, alternately, how do I get all my files to the same audio level?
It would be less tedious to use Normalize. Then you won’t have to adjust the value each time.
Also bear in mind that neither effect will make the files “equally loud”. They do nothing except affect the peak volume.
If you are exporting to MP3 or another lossy format - you don’t. Audio data is discarded by the lossy encoding. It is a feature request for Audacity to attempt to force the peak level to be the same. That said, OGG tends to suffer less from volume changes after export.
Export to a lossless format like FLAC or WAV and accept the file size is larger.
Gale
See if your audio player support “ReplayGain” or “Sound Check”. If it does, then use that and save yourself a lot of bother 
Both of these technologies just require a quick scan of each audio file, and can then automatically adjust the playback level.
See: http://en.wikipedia.org/wiki/ReplayGain
(“Sound Check” is the Apple version, available on most iPods)
Thank you, Gale, and Steve.